xs400 ignition comes and goes

Dug the bike out of the shed this spring, got her fired up and she ran like a scalded cat during the 10 mile trip to my parents' place. Hours later, I hop on and crack her off, only to find that the bike REFUSES to run above an idle. It idles just fine, but as soon as you hit the throttle it misses and bogs and just hangs there. I took apart the carbs and cleaned them *they really weren't dirty* put it back together and same thing. So I pulled the plugs one at a time and watched while it ran, and as soon as i would twist the throttle, the right plug's spark would cut out and get very erratic. I resistance checked the coils, they check out. I tried to check out the pickup coils on the crank, but couldn't really find a place to connect to test them, so gave up. Put it all back together and it runs like nothing's happened.

Fast forward a bit and I'm riding down the interstate when, like flipping a switch, the bike just starts dragging on the motor. Same thing, idles fine, but wont do anything more. I park it at a local business and come back for it later with a truck, but when I start it it runs fine and I ride back home. Twice on the ride home it started acting up and nearly stopped, but pulled out of it in time for me to keep heading down the road. (Once it let go a pretty nasty backfire)

I'm posting for a diagnosis. I've been told by some it's the TCI box, others say no. I did accidentally leave one plug wire off for a while when I was running it down the road right after it came out of the garage (wondered why it didnt have any power ) not sure if that could damage the ignition system. All I know is i want my 60+mpg bike back on the road! Any help is appreciated, thanks.

 

Start with the fusebox. It could be any wiring connection between there and the sparkplugs; it COULD be a TCI issue as well but the fact that it keeps "clearing up" indicates it's more likely a bad connection somewhere.

 

Well I've gone through every plug and connector I could find (none seemed particularly dirty or corroded) on the wiring loom, and the bike seems to be running fine now, so I guess it's good until the next time it leaves me on the side of the road :wink: Will post back with any updates. Any other gurus want to comment?

 

+1 on checking the fusebox. Corrosion in stock fuse boxes is a well known problem. Most of the time you can't see the corrosion, unless the bikes served a few years as a boat anchor. Replace it ASAP if you haven't yet.

The TCI gang plugs are also a common trouble spot. Just wiggling them is not enough; you will need to make damn sure they're clean. It also helps to stuff some dielectric grease in the connectors before you plug them back in to keep the moisture out.

A faulty kickstand switch (if you have one) could also give you grief when you're in gear.

 

I pulled my ignition cables off of the spark plugs, looked down inside the cap, removed the connector by unscrewing it and found a small link that transfers the spark between the cable and spark plug connector. On my XS400, I had some corrosion, so i cleaned them up with scotch bright and that helped a lot! My problems at the time was rough idle.

 

I'm having this exact problem all of a sudden. Last ride was 100% perfect, parked it for a week and now it misses above 3k rpm, idle is perfect, but won't go above 3k.

I didn't touch the bike from last it ran till the issue now.

i'm a little stumped... and pissed...

 

Update, i'm losing spark on the left hand side when it misses. Going to check wiring right now, will report back.

 

Still no solution, check wiring from tci to coils, everything is fine. It's now anything above 2k rpm it loses spark (like everyother fire).

Generator is kicking out 13V at 1.2k idle.


I'm at a loss guys, thoughts?

 

Guess i'll check my coil resistances tomorrow.. see what that tells me. It did get close to 0 degrees here the past week.

 

Hopefully this:

http://www.jetav8r.com/Vision/IgnitionFAQ.html

Will arm me with all the knowledge i need to troubleshoot this.

REALLY good read!

 

I must have a failed TCI i have the following readings:

All written as L then R (ohms)

Pickup coils: 114.6 - 115.9
Pri Winding: 4.0 - 3.8
Sec Winding 8.4k - 8.27k
Plug Caps 11.45k - 10.65k

Only thing that seemed out from the '82 seca manual was the pri.

Manual says 2.75 +- 10%, I get 4 and 3.8
But it'll run idle perfect all day, so i think it's prolly the transistor in the TCI.

Must be old and broke down enough it can't switch faster than 2k.

 

ok KRS14 and Volkswaggonette, can either of you or both check to see if all your pipes get hot at the same time after a cold start? I've been BATTELING this for 15 months, did carbs, cyl boots, air box boots, ignition, fuse box, valve adjustments, only thing i haven't inspected or replaced is the TCI. I also have the same problem, BUT, sometimes different cylinders will not fire, sometiems, 3, 1, then 2 - NUTS. If your willing to check just use your two hands on all 4 header pipes. Thanks

 

OR.... it could just be a sneakilly bad solder joint......

*Solved*


but i'm still pissed, cause everything read fine connection wise.

 

My bike would run fine at idle, just couldn't get the current back through the solder joint i'm assuming.

Does your issue stay for a while on one cylinder, or is it completely random?

 

completely random. Where was the solder joint? on TCI PCB (printed circuit board)?

good job btw. I'm about to ask if anyone has a spare TCI for me to test with

 

Ya, TCI, but I dunno which one, i remelted all of em, and made sure i didn't have any bridges.

 

well i just took a resistance reading on # 1 plug wire up to the new coil and there was none, it was open. the wire that comes out of the plug wire and gets bent under the connector was broken. is that enough not let the engine rev when the throttle gets opened? I would think the answer is No since I've heard of bikes running on 3 cyls...

 

AND FOUND THE SAME THING ON # 3!!!!!!!!!!!!!!!!!!! auto part store doesn't open till tmrw - gerrrrrrrrrrrr. damn neighbors would be complaining anyway by the time I got back and got it done. But I'm off tmrw

 

Do you mean the meter said 0, that means NO resistance. Also, are you measuring from ground to the spark wire (without the plug cap on). This should read about 7-8k ohm, If you had your meter set to say 200 ohm range it will read as infinite resistance. Make sure you were in the correct range if this is what you were doing.

you mean the center conductor in the plug wire from the coil to the cap. I've never seen one bent outside the wire when the plug cap gets screwed on. It's usually just left flush with the cut, and you screw the cap onto the wire. The screw part of the cap connects to the center conductor inside the wire itself.

It very well could be that you just need to refresh your solder in the TCI, could have a cracked joint from 26 so years of age You don't have to add any solder, just heat up the solder on the joints as they are.

May help Just don't bridge any connections!!